Corrupt file during download from modem

Has anyone experienced a user who dials into a SHIVA box and attempts to download a file to a nT 4.0 server, but gets the following error:

NOTE: Its not all the time, and it happens to different users. Out of 70 downloads a week 10 get corrupt.
System was attempting to transfer file data from buffers to \server\user\user.zip The write operation failed and only some of the data may have been written to the file.